The invention relates to window coverings and particularly to a light control window covering having strips or slats that can be tilted from an open position to a closed position to control the amount of light which is admitted.
Venetian blinds are well-known window coverings. They have a series of horizontal slats hung from ladders which extend between a headrail and a bottom rail. The slats can be rotated between an open, see through position and a closed position. Additionally, the blinds can be raised and lowered. Venetian blinds contain aluminum, plastic or wood slats and are available in a limited number of colors.
Draperies are another common window covering. Draperies are available in a variety of materials and colors. Commonly a designer will provide a sheer curtain which permits some passage of light in combination with a heavier drapery through which light cannot pass. Consequently, the owner of that drapery system may have a completely open window, a window covered by the sheer which allows for daytime privacy, some passage of light and a view of the outside; or a window covered by the heavier drapery and a sheer which allows night time privacy, little passage of light, and no view of the outside.
In U.S. Pat. No. 3,384,519 to Froget and U.S. Pat. No. 5,313,999 to Colson et al. there are disclosed cellular type window coverings having first and second parallel sheer fabric sheets hung from a roller. A plurality of light impeding or somewhat light impeding vanes extend between the sheer fabric sheets. The vanes are angularly controllable by relative movement of the fabric sheets. Like the combination of a sheer fabric and a light impeding fabric, these system allow the user to have a fully open window, a sheer covered window allowing light transmission with daytime privacy, and a covering providing night time privacy or room darkening. In addition, such systems have intermediate light control of a louvered product like venetian blinds. Both the Froget and Colson window covering systems are difficult to fabricate, have a very flat appearance when in the closed, light impeding position, can only be tilted in one direction and can only be tilted when completely deployed. They also have a very limited selection of fabrics because three layers of fabric must wrap around a tube with the back layer traveling much farther than the front layer.
Judkins in U.S. Pat. No. 5,339,882, discloses a window covering having a series of slats connected to two spaced apart sheets of material. In one embodiment, the slats are attached to tabs extending inward from each sheet. The slats are substantially perpendicular to the sheets of material when the covering is in an open position. The slats are substantially parallel to the first and second sheets of material when the window covering is in a closed position. This product does not roll up readily and is intended to be raised with lift cords.
In U.S. Pat. No. 5,205,333, Judkins discloses a cellular shade formed by attaching an accordion pleated shade to a tabbed sheet. In this shade the tabs extend outwardly.
Pleated cellular window coverings have a spring take-up in the pleat. It is desirable that the cellular structure have a fullness in the pleat and that the face of the structure not go flat. The front face need not be equally spaced from the back face across each cell, nor must the front cell wall have the same height as the back cell wall. Indeed, it is sometimes desirable to have a shorter back wall to keep fullness in the front. Any side to side variances are hidden by the fullness of the pleat. However, in a window covering of the type disclosed by Colson in U.S. Pat. No. 5,313,999 the opposite is true. It is important that the fabric faces be nearly flat and the vanes be equally spaced from side to side and front to back. Since light passes through the cells, variances in cells are readily apparent and detract from the closure.
Most woven and knitted fabrics are not uniform. They go askew, have a bias or have a belly in the middle or sides. This lack of consistency is particularly common in the very soft, light body, sheer fabrics that are most desirable for this type of product. If a cellular structure is formed from most woven and knitted fabrics using conventional bonding practices, the excess material tends to bulge or form a bag. This bagging causes the cells to be non-uniform. Yet, non-uniform cells are undesirable in a light control product. Consequently, there is a need for a method of forming light control window coverings with uniformly sized cells. Such a process must compensate for the irregularities found in most woven and knitted fabrics.
Lift cords are required in those cellular products which are not attached to a roller. Because some customers find lift cords detract from the appearance of the shade, most fabric light control window coverings are being offered on rollers. Yet, lift cords allow tilt in both directions, tilt in intermediate positions, and bottom and top stacking shades. Lift cords even allow non-rectangular shades to tilt. Consequently, there is a need in the marketplace for cellular products and particularly light control cellular products having lift cords which are not noticeable. There is also a need for a light control window covering having two sheets of sheer fabric connected by light impeding vanes which is controllable by lift cords and which can be tilted in either direction even when the product is partially stacked. Additionally, there is a need for light control window coverings that can be made as arches, slant tops, and other non-rectangular shapes and can be used in a wide variety of specialty applications.
We provide a light controllable window covering in which there is an outwardly or inwardly tabbed front sheet and a back sheet which preferably is also tabbed outwardly or inwardly. As the outwardly facing tabs are formed one edge of a vane is inserted between the segments of the sheet that form each tab. The tabs are bonded in a manner to assure uniform length of the material between tabs to maintain uniform cell size. Frequently, maintaining uniform cell size for light transmissive fabric creates a tab having a curved outer edge. This is usually not noticeable because the tab is perpendicular to the viewer. However, we prefer to trim the tab as it is bonded to create a uniform width in the tab, especially for tabs formed in the front sheet. If desired, the outwardly facing tabs could be trimmed off entirely or trimmed to be only a few thousandths of an inch in width.
We further prefer to provide a striated fabric for the back sheet and optionally the front sheet of the window covering. This fabric has vertically oriented striate yarns having a diameter close to the diameter of the lift cords. As a result the lift cords are hidden.
Other objects and advantages of the present invention will become apparent from the description of certain preferred embodiments shown in the drawings.